The nonrecurrent laryngeal nerve: anatomic and electrophysiologic algorithm for reliable identification.

OBJECTIVES/HYPOTHESIS The recurrent laryngeal nerve (RLN) intraoperative monitoring (IONM) provides a new functional dynamic that adds to visual identification of the RLN to optimize its intraoperative management. Intraoperative monitoring has been applied to the initial identification of the RLN. We now apply IONM to the identification of the nonrecurrent laryngeal nerve (NRLN) and provide electrophysiologic and anatomic parameters to facilitate this technique of neural identification for the NRLN, which is at increased risk of injury during thyroid surgery. STUDY DESIGN Retrospective. METHODS A study of cases of the NRLN from consecutive thyroid surgeries with IONM was conducted. Preoperative and postoperative laryngoscopy was documented in all cases. RESULTS Ten right-sided nerves (0.6%) were identified as NRLN. One hundred percent of NRLNs had documented normal preoperative and postoperative laryngeal function. Distal and proximal vagal nerve stimulation points that allowed for the electrophysiologic prediction of a nonrecurrence in all patients were identified. Electrophysiological normative parameters of NRLN were compared to those of the normal right RLN and right vagus nerves. CONCLUSION Nonrecurrent laryngeal nerve is present in 0.6% of patients undergoing thyroid surgery. Intraoperative monitoring involving vagal stimulation at the defined distal and proximal points provides reliable electrophysiologic intraoperative verification of the presence of the NRLN. Three anatomical subtypes of right NRLN are noted that enable early identification of the NRLN. In conjunction with detailed knowledge of the NRLN anatomic pathways, they also may be helpful in preventing injury to the NRLN, which has been shown to be at higher risk during thyroid surgery. We provide an anatomic and electrophysiologic algorithm for reliable identification of the NRLN. LEVEL OF EVIDENCE 4.